Method of and apparatus for manufacturing nitrogen



March 18, 1947. w, LAlRD 2,417,558

METHOD OF AND APPARATUS FOR MANUFACTURING NITROGEN Filed Jam 10, 1942 61d. MAXSOA 44 7 Z v Arm/aw Y Patented Mar. 18,1947

METHOD OF AND APPARATUS FOR MANU- FACTURING NITROGEN Alfred W. Laird, Oak Park, and Gordon J. Maxson,

Western Springs, Ill., assignors to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application January 10, 1942, Serial'No. 426,368

2 Claims. 1

This invention relates to a method of and apparatus for manufacturing nitrogen and more particularly to a method of and apparatus for manufacturing nitrogen free from active gases for use in connection with heat treating furnaces. It has been known that nitrogen could be prepared by heating copper to a relatively high temperature in a retort and passing dry air through the retort to remove the oxygen, but in following this practice, the copper was discarded and this process was not adaptable to commercial use. Usually the copper would become sintered or disintegrated and solidify or collapse in the retort and could not be restored to a useful state.

It is an object of the invention to provide a simple and efiicient method and apparatus for economically manufacturing nitrogen.

In accordance with one embodiment of the invention a nitrogen separator is provided in connection with a circulating and recirculating pipe system for the production of relatively pure nitrogen for use as a protective atmosphere in a heat treating furnace. The nitrogen isproduced from air contained in the system, or admitted to the system, by circulating thegasthrough one of a pair of dryers to remove the moisture from it and then through one of a pair of copperfilled reaction chambers to remove the oxygen. .The gas thus produced is then pumped into a furnace, where it forms a protective atmospherearound work being treated and then is redirected back to the copper filled chamber. The duplicate dryer of the pair of dryers and the duplicate copper filled reaction chamber may be put into service when the other dryer and copper filled reaction chamber require. reactivation. When i bar and dryer are switched into communication with the furnace or furnaces which they are supthe change is effected, a reducing gas comprising a mixture of partially burned natural gas and air is passed through the copper filled reaction chamber to reduce the copper in the reaction chamber while the dryer, which may be in the form of an activated alumina dryer, is being reactivated by heat and the passage of air through theactivated alumina. The copper filled reaction chambers comprise retorts in which copper wireof'19 to 21f gage, cut to from two to fourinch lengths, which has been packed under a pressure ofapproximately 175 pounds per square inch may be heated to from 1200 to 1400 F. and the dryers are provided with heat elements-imbedded in the material in the dryer, whereby they may be heated when being reactivated. In the practice of theinvention, the" oxidation of the copper is halted prior to completeoxidation thereof and the duplicate copper reaction champlying with nitrogen and the copper in the previously used retort is restored to its elemental condition as stated hereinbefore. In this manner, the copper will retain its original shape and will be completely reduced. j

,A better understanding of the invention may be had by reference to the following detailed description when considered in conjunction with the accompanying drawing, wherein the single figure shows, diagrammatically, a nitrogen segregating or preparing apparatus and the pipe system for connecting that apparatus to a heat treating furnace to supply a protective atmosphere in the heat treating furnace.

By reference to the drawing, it will be seen that there is provided a heat treating furnace which comprises a body of insulating material 2 enclosed in an outer shell 3 and provided with an inner shell 4, which defines the limits of a heat treating chamber. In the inner shell 4, there are provided heating elements 5 and 6 which are located in the chamber thus formed for supplying heat to the furnace. In communication with the chamber formed by the shell 4, there is provided a suitable elevating mechanism 8, sealed from the outside atmosphere, for raising and lowering a work supporting platform 9 to carry the work between the furnace l and a quenching bath Ill. The bottom of the chamber formed by the shell 4 may be substantially closed by means of gate members II and I2, a small passage l3 being maintained between the gates I I and I2 to permit any gas forced into the upper portion of the furnace to pass downwardly through a loading chamber l l to an outlet, to be described. The gatesil and I2 are slidable in guideways l5 and I6, respectively, and may be manipulated by means of rods l1 and [8, respectively, to prevent any appreciableloss of heat from the chamber formed bythe shell 4. The chamber I4 is provided with a loading door 25, whereby, when the platform i2 is in position just beneath the door 25, parts may be loaded on to the platform 9 and the chamber [4 extends down into the quenching bath l0 which is contained in a container 26. The structure described thus far comprises a heat treating furnace of the type described in detail in the 'co-pending application of G. J; Maxson, Serial No. 426,369, filed January 10, 1942. This furnace may be supplied with a protective atmosphere in the form of nitrogen essentially free from active gases by the apparatus to be described hereinafter.

The upper end of the chamber formed by the inner shell 4 is in communication with a pipe 30, through which the protective gas may be supplied to the furnace and the chamber l4 has in communication therewith a pipe 3|, through which the protective gas may be drawn out of the furnace. The gases in the system 'as a whole are circulated by means of a pump 32, which at the beginning of the operation of the apparatus, will draw the air from the furnace chamber and from the outside atmosphere, through pipe 3| and an inlet port 33, in a mixing chamber 34. The outlet aperture of the pipe 3| -is reduced'in size to form an orifice 35,whereby pressure is maintained in the furnace despite small leakages in the system as a whole. Any nitrogen and other gases which may be in the furnace orthe. air which may be in the furnaces or which may be drawn through the inlet port 33 are forced by the pump 32 under'pressure out through a pipe 36; The pipe 36 terminates in afour-way valve 39, shiftable to connect the pipe 36 to either a pipe 31 or a pipe 38'. In the position shown, the valve 39 connects the pipe 36 to the pipe 31 and, hence, any gas pumped by thepump 32 into pipe 35 will be directed, through pipe 31, to an activated alumina dryer 40, in which there are'positioned heating units 41-41. Similarly, the pipe 38 feeds into an activated alumina dryer 42, having heating elements 4343 in'it. The upper ends of thedryers 40 and 42 have pipes- 44 and 45' extending from them toa four-way valve'46, which may be shifted to connect either thepipe 44 or the pipe'45 with a pipe '41, which extends to a; four-way valve 48, shiftable to direct the gas from the dryer being used to'either a; pipe 49 or a pipe 50 leading to retorts 51 and 52, respectively. The retorts and'5'2 are filled with copper wire'of 19 'to 21 gage; cut to lengths of? we inchesand packed in'the retorts under a, pressure of approximately 175 pounds per square inch so as to present a large surface area relative to the space which it occupies.

In the preferred form of the invention, the retorts 5| and'52 are formedof relativelyheavy gage copper, nickel plated on the outer'surface toprevent oxidation and scaling thereof; The retorts5l and 52 are positioned withinheating chambers 53' and 54, in which there are placed heating elements 5555 and 56-56, respectively, for heating the retorts5i and 52 to a temperature of from 1200 F. to 1400 F. and, preferably, to"11350 F. In order to distribute the flow of gas uniformly through the copper packing; grills are provided at the top and bottom of each retort.

The Va1ve'48, in the position shown; Will direct the'gases from pipe 41 into retort 5|, which com municates at its upper end with a pipe 5'! extending to a four-way valve 58, shiftable to connect' the pipe 51 or the pipe 59 leading from the upper end of retort 52 to the pipe 30, extending. to the treating furnace. In the position shown, the valves 39, 45, 48 and 58 are set to direct the gas pumped through the pipe 35through the dryer 40 and retort 51 to the furnace. If the Valves are all shifted to their opposite positions, the gas from pipe 36' will be directed, through dryer 42 and retort 52, to the furnace. In the position shown, the valve 39 also serves to connect the dryer 42, through pipe 38, with a pipe 60, which may be connected to a, pump or other means for supplying air to the dryer 42 and, through the dryer 42', pipe 45,.and valve 46, to a pipe 6| open to the atmosphere. In this manner, while the dryer 40 is being utilized to remove moisture from the gas pumped to the furnace, the dryer 42 may be reactivated by passing reactivating air through it while heating it to approximately 350 F. by means of heating elements 43-43. Thus, the gas passing from the pipe Bl will be moist air, and the moisture absorbed by the alumina during the use of a retort will be driven from the alumina while the other retort is in use.

In the position shown, the valve 48 will interconnect the retort 52 through the pipe 50 and a, pipe 62 to a retort 63 positioned in a heating chamber 54, having heating elements 65-55 in it. The'gas supplied to the retort 63 comprises a mixture of natural gas and air admitted to the retort through pipes 66 and 6?, respectively, which both feed into a pipe 58 extending into the'top'" of the retort 63. Thus, with the apparatus in the position shown, the dryer 42 is being reactivated by passing air through it to the outside atmosphere while the dryer is heated by the heating units 43 and the oxidized copper-in retort 52 is being reduced by a gas prepared from partially burned natural gas and air supplied from the retort 63, through pipe 62, valve 48, pipe 50, pipe 59, and the valve 58 to a pipe 09 open to the atmosphere.

Any suitable reducing gas, such as pure hydrogen, charcoal gas or suitable mixtures 'of'par tially burned gas andair, may be used-to restore the copper in retorts 51 and 52 to its elemental condition. In thepreferred form of the invention, a, gas having a dew point of 0 centigrade' and comprising; 35% Hz, 20% CO, 0.5% C02, 0.75% CH4, and the balance nitrogen has-been found satisfactory.

In the operation of the apparatus, the valves 39, 48,- 48 and 58 may be set in the position shown or in the position opposite to that shownto supply relatively pure nitrogen to the heat treating furnace l and at the same time that either dryer 40 ordryer 42 and one of the copper filled'retorts 5! or 52 is supplying nitrogen to the heat treating furnace, themoisture gathered in the dryer may be discharged therefrom and the copper in the idle copper filled retort may be restored to its elemental condition. In this manner, except for the very short period when the valves are being shifted from one position to another, acontinuous supply of pure nitrogen containing a trace of -carbon dioxide will be supplied to the heat treating furnace. Ithas been found that in using the system described hereinbefore, nitrogen will'be produced containing a maximum of 0.2% carbon dioxide as the major impurity. It hasbeen found an atmosphere of this type is neither decarburizing nor scaling to tool steel at heat treating temperatures.

Furthermore, it has been found'advisable to feed the gases through the dryer and heated copper filled retorts at the maximum rate of 3cubic feet per hour and, preferably at approximately'one' cubic foot per hour, for each square. inch of cross section of the copper filled retort. When the apparatus as described hereinbeforeis being used, ithas also been found'that the period necessary for the reactivation of one retortduring. the utilization of the other retort is approximately one-seventh the time required to oxidize the copper in the retort to anextent where it requires reactivation. The length of the retorts 5| and'52 will determine the length of time a retortmay be used before it requires reactivation. Thus, with the apparatus described, a substantially continuous supply of high purity nitrogen may be fed under pressure to the heat treating furnace or furnaces to maintain a protective atmosphere therein during the heat treating, and, if desired, subsequent quenching of the tool steel in a nitrogen atmosphere may be effected by simply lowering the platform 9 carrying the material to be treated into the chamber 14 and maintaining it there until sufficiently cool to warrant its removal from the furnace. When the temperature of the copper filled retorts 5| and 52 is maintained within the limits pointed out, i. e., 1200 F. to 1400 F., and the flow of gas through the said retorts is maintained at approximately the rate pointed out hereinbefore, the copper oxide formed will hav sufficient mechanical strength to maintain its shape and form and the hereinbefore described treatment thereof will restore it to substantially its original condition.

Although a specific embodiment of the invention has been described hereinbefore, it will be understood that numerous modifications thereof may be made without departing from the invention.

What is claimed is:

1. An apparatus for maintaining an atmosphere of nitrogen in a furnace at a pressure higher than atmospheric comprising a treating furnace, a pair of heated retorts in parallel arrangement adapted to contain comminuted copper, a pair of dryers in parallel arrangement, valve and conduit means operating to alternately interconnect a dryer and a retort in series with the furnace and to shut oil the other retort and dryer therefrom for re-generation, a pump arranged to recirculate furnace atmosphere through the dryer and retort in series, and automatic means opening to the atmosphere between the inlet of the pump and the furnace arranged to admit air to the inlet of the pump on a drop of pressure in the furnace.

2. The method of supplying nitrogen to a heat treating furnace, which consists in heating a mass of copper particles in a retort to a temperature of from 1200 F. to 1400 F., passing atmosphere co'iitaining oxygen and nitrogen over the hot copper at a rate of from one to three cubic feet per hour per square inch of cross sectional area of the retort, and maintaining the pressure of the nitrogen in the furnace above atmospheric.

ALFRED W. LAIRD. GORDON J. MAXSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,078,423 Frank et al. Nov. 11, 1913 1,547,688 Romanelli July 28, 1925 1,968,442 Clark et a1. July 31, 1934 914,279 Hurford Mar. 2, 1909 984,605 Reichel et al Feb. 21, 1911 1,869,025 Seastone July 26, 1932 2,269,392 Bahney Jan. 6, 1942 FOREIGN PATENTS Number Country Date 16,963 Br. 1908 10,581 Br. 1906 20,631 Br 1909 218,671 German Nov. 25, 1908 

